In the field of microelectronic devices, which includes the fields of integrated circuits, optical devices, memory devices, magneto-electric components, and other micro-devices or microdevice components used in electronic, memory, optical, and similar applications, a microelectronic device is prepared by multiple steps of depositing and removing combinations of materials onto a substrate. A material of a layer applied during processing may be a conductive material such as a metal, a semiconductor material such as a silicon-based material (e.g., silicon oxide), or a polymeric material. The microelectronic device is prepared by selectively applying and selectively removing these materials at a surface of a substrate in a manner that builds layers of microelectronic structures onto the substrate. Between these steps, many of the applied material layers are processed by steps of planarizing or polishing the uppermost (surface) layer of the substrate. Examples of microelectronic device substrates that require a planar surface during manufacturing include substrates used to produce integrated circuits, memory disks, magnetoelectric microdevices, and the like. Examples of metal and semiconducting materials that are placed onto and removed from a surface of a microelectronic device substrate include tungsten, cobalt, nickel, copper, metal alloys (e.g., Al2O3, NiC, TiC), oxides such as silicon dioxide, among others. In many instances, a conductive material, e.g., a metal such as tungsten, copper, or cobalt, is placed onto a substrate to cover or fill underlying structures previously prepared at a surface of the substrate. After placement of a layer of conductive material, an excess portion (e.g., “overburden”) of that material must be removed to leave behind a remaining amount of the conductive material that forms conductive features of a microelectronic device.
A common technique for processing a surface of a microelectronic device substrate is by chemical-mechanical planarization (CMP). The terms “planarizing” and “polishing,” and other forms of these words, although having different connotations, are often used interchangeably, with the intended meaning conveyed by the context in which a term is used. For ease of description, such common usage will be followed herein, and the term “chemical-mechanical planarization” and its abbreviation “CMP” will be used to convey either of the more specific terms of “chemical-mechanical processing” and “chemical-mechanical polishing.”
In chemical-mechanical planarization, a substrate is held by a carrier head or “carrier,” and a surface of the substrate is pressed against a surface of a CMP pad, typically in the presence of an abrasive material such as an abrasive slurry. The pad is mounted on a platen that opposes the substrate surface, and the substrate surface, held by the carrier, is moved relative to a surface of the pad by placing the carrier and substrate, the platen, or both, in motion. As desired to effectively and efficiently remove material from the substrate, the slurry may contain a combination of chemical materials and abrasive particles so that the motion between the substrate surface and the pad, in the presence of the abrasive particles, chemical materials, or both, causes removal of desired amounts and types of materials from the substrate surface, ideally to produce a planar or polished surface. Typical slurries for removing metal from a substrate surface can include a high amount of a liquid carrier in which chemical materials and abrasive particles are dissolved or dispersed. The abrasive particles can have size and composition features to be useful for removing a specific material from a substrate; example particles may be made of or contain alumina, ceria, silica (various forms), or other metal or metal oxide materials. The chemical materials of the slurry are selected to achieve a desired removal rate and final topography (e.g., smoothness) of the finished substrate surface, and the types and amounts of the chemical materials in a slurry can depend on the type of material or materials present at the substrate surface. Examples of chemical materials include organic chemical materials that function as one or more of a surfactant, oxidizer, organic inhibitor (to control a removal rate), chelating agents, and other chemical materials that contain an organic group. Other possible chemical materials include pH adjusting agents (base, acid), and biocide (as a preservative).
Many CMP processes that remove a conductive metal from a substrate surface use a two step process. A first step is used for aggressive removal of a layer of metal “overburden,” and is performed to effect a relatively high removal rate; this step is often referred to as a “bulk removal” step. A subsequent step is performed to refine or “polish” the surface after the bulk removal step, this step often being referred to as a “polish” step. The bulk removal step is performed with a slurry that includes abrasive particles and chemicals selected to produce a high removal rate. High selectivity during a bulk removal step to remove metal relative to other materials (e.g., silicon oxide) may not be required or emphasized. The subsequent polishing step is commonly performed with a slurry that includes different (e.g., less aggressive) abrasive particles and different chemical materials compared to a slurry used in bulk removal step. During a polishing step, more selective removal of one type of material (e.g., a metal) relative to a different material (e.g., silicon oxide) may be important, and a high rate of removal of a material is less important. Also, different processing parameters may be used with the two different types of steps, such as different speeds of relative motion between the substrate and the pad, different pressures between the substrate and the pad, and different processing times. Desirably, and by current conventional practices, the bulk removal step is performed without removing the substrate from the carrier; i.e., the substrate is placed in a carrier for processing by the bulk removal step, and the substrate is held in the same carrier for processing in the polishing step.
The polishing step is generally followed by a “post-CMP” cleaning step, during which the substrate is physically removed from the carrier and transferred to a cleaning apparatus that further cleans the substrate surface by means that may include a brush cleaning station, at which the substrate is mechanically scrubbed and rinsed, also in the presence of a CMP cleaning solution.
With many CMP processes, residues accumulate at a substrate surface and can be present at the substrate surface both during and after a processing step. Significant efforts are made to prevent the formation of residues, or to remove residues once present, because efficient processing of the substrate to a defect-free finished device relies on the existence of a highly refined and clean substrate surface for processing during subsequent deposition and removal steps. Residues materials that contain abrasive particles in particular must be removed because these can produce surface defects such as scratches, as well as device defects in the form of embedded particles.
A variety of possible residue types may be present at a substrate surface following a planarization or polishing step. A residue might include one of the materials that make up a slurry, e.g., a chemical material or an abrasive particle, alone or in combination. A residue might also include a material that becomes introduced to the slurry during a CMP process step, such as a material that becomes removed from a substrate surface during processing (e.g., a metal ion) or that is generated during processing by reaction or chemical modification (e.g., oxidization or reduction) of a chemical material of the slurry. Certain solid, e.g., particle type, residues are formed during a processing step if two such materials combine or interact in a manner that causes the two to produce a solid, for example by precipitating out of solution, by agglomerating, or by coagulating to form a solid residue particle (also referred to as “residue particles,” for short). Examples of these types of residue particles can form when an organic chemical material in a slurry interacts with a metal material in a manner by which the two materials form a solid (e.g., agglomerate, coagulate, or precipitate). The metal material may be a metal abrasive particle, a metal-containing abrasive particle (e.g., a metal oxide), a metal ion, or another metal-containing material in the slurry that can combine with the organic chemical material to form a solid residue particle by precipitation, agglomeration, or a coagulation. Many slurries contain organic chemicals that can be attracted (chemically, ionically, etc.) to a metal material.
Solid residue particles are problematic if they are attracted to a surface of a CMP substrate to a degree that the particles will stubbornly adhere to the surface. When such residue particles are present at a CMP substrate surface, an additional processing step may be required to dissolve the residue particles or to physically remove the particles from the surface. Examples of such steps include an added cleaning or rinsing step (“in-situ cleaning”) performed at an end of a CMP process step (e.g., a bulk removal step, a polishing step, or the like), without removing the substrate from the carrier used to perform that CMP process step. The cleaning or rinsing step may typically use the same carrier, platen, and pad as the preceding step (or a subsequent CMP step), but involves a cleaning solution that does not contain abrasive particles. The cleaning solution may instead contain only deionized water or deionized water with optional organic solvent, pH adjusting agent (acid or base), surfactant, or chelating agent, to dissolve or rinse away the solid residue particles.
The problem of residue particles formed by a combination of two or more materials present in a slurry, during a CMP process step, can be exacerbated by contamination of materials between earlier and later processing steps in a series, especially if the steps are performed on a substrate that is held in the same carrier for both of the earlier and the later steps. During a series of CMP steps, chemical materials or abrasive particles may remain at a surface of a substrate or at a surface of a substrate carrier, at an end of a first or earlier step. These materials can be carried to a subsequent step on the substrate surface or the carrier. If one or more of the materials from the previous step are not compatible with materials of a slurry of the subsequent step (e.g., can combine with a material that is or becomes present during the subsequent step to coagulate, precipitate, or agglomerate), residue particles are produced during the subsequent step.
Example CMP processing methods that include multiple steps, that are susceptible to contamination of a later step by materials of an earlier step, include multi-step (e.g., two-step) processes for removing metal from a substrate, which include a first bulk removal step followed by a subsequent polishing step on the same substrate. The abrasive particles and the chemical materials of the slurry useful for performing the bulk removal step are designed to provide desired results of a bulk removal step, including a high removal rate for the metal material being removed. The chemistry of the slurry for the subsequent (polishing) step does not require a high removal rate, but is intended to provide a more gentle removal of material and, often, high selectivity in removing one type of material from the substrate versus a different type of material also present at the substrate surface. For efficiency, these multi-step processes are preferably performed using different platens and pads, but with the substrate being held using the same carrier for each step. The carrier will be used to hold the substrate to engage the substrate with a first platen, with use of a first “bulk removal” slurry. The carrier will then transport the substrate to a second platen, which will perform a polishing step using a second (polishing) slurry that has different abrasive particles and chemical materials. The carrier, the substrate, or both, can physically transfer chemical materials, abrasive particles of first slurry, or chemical materials produced during the first step, to the second step, i.e., can contaminate the second step with materials of the first step.
Existing techniques for removing residues from surfaces of CMP substrates during a CMP process, e.g., “in-situ cleaning” techniques, can be effective with certain types of residues on certain substrates. The effectiveness can depend on the type of residue (chemical, particulate, agglomerate, coagulate, precipitate, etc.), its chemical and physical makeup and structure, the type of substrate and degree of attraction between the residue and substrate surface, and whether or not the cleaning solution is effective in breaking down or dissolving the residue particle or disassociating the residue particle from the substrate surface. Existing techniques are not generally or completely effective to remove all types of residue particles, especially residue particles that contain both an organic material and an inorganic material that combine to form a residue particle structure. Significant need continues to exist for new and more highly effective cleaning solutions and in-situ cleaning steps for removing these types of residue particles from CMP substrate surfaces.